Comparison of Fetal Cerebellum and Cisterna Magna Length by 2D and 3D Ultrasonography between 18 and 24 Weeks of Pregnancy.

To compare the fetal cerebellum and cisterna magna length measurements by means of two- (2DUS) and three-dimensional (3DUS) ultrasonography using the three-dimensional extended imaging (3D XI), a cross-sectional study with 69 healthy pregnant women between 18 and 24 weeks was performed. For the measurements by 2DUS, the axial planes were used and for the 3DUS a sequence of adjacent axial slices (multislice view). To evaluate the difference between the two techniques, we used the Wilcoxon test. To evaluate the correlation between the cerebellum and cisterna magna length measurements and the gestational age, we used the Spearman correlation coefficient (r). For the calculation of reproducibility, we used the intraclass correlation coefficient (ICC). The mean of the transverse and anterior-posterior diameter of cerebellum and cisterna magna by 3DUS was 9.23 and 6.62 mm, respectively. It was observed that the average of the measurements obtained by 3DUS was significantly higher, 0.76 and 1.02 mm for the length of the cerebellum and cisterna magna, respectively (P < 0.001). There was a high correlation between the length measurement of the cerebellum 3D (r = 0.940, P < 0.001), but low correlation of cisterna magna 3D (r = 0.462, P = 0.080) with the gestational age. There was good intra- and interobserver reproducibility for the cerebellum and cisterna magna 3D with ICC = 0.792 , 0.668, 0.691, and 0.287, respectively. The measurements of the fetal cerebellum and cisterna magna length by 3DUS using the software 3D XI were significantly higher than those obtained by 2DUS.